In recent years, in a printer market, the printer has been being shifted from a monochrome printer to a color printer. However, a price of a color print or a color copy is still high and it is a present situation that a color original is often copied or printed as a black-and-white image.
Among them, when the color original is copied or printed in black and white or a monochromatic color, generally, the original read by a reader constructed by a plurality of channels of red, green, and blue is image processed into one black channel. A process for converting the read color image into the black channel is hereinbelow called “color/monochrome conversion”.
With respect to the color/monochrome conversion, a method whereby a color original is separated into characters, an image, and a background and is converted into a color monochrome image so that only the characters can be easily read has been disclosed in the Official Gazette of Japanese Patent Application Laid-Open No. 2003-283848. Specifically speaking, luminance of monochrome character data is compared with luminance of either monochrome image data or monochrome background data, thereby obtaining a luminance difference. A method whereby when such a luminance difference is equal to or less than a predetermined value, the luminance of the monochrome character data is changed in such a direction as to increase the luminance difference has also been disclosed.
In the ordinary color/monochrome conversion, there is such a problem that when a character drawn in yellow in the color original is copied or printed as a black-and-white image, the obtained character becomes difficult to be seen. Therefore, a blend ratio of the read signals of red, green, and blue is set to a blend ratio in which reproducibility of a yellow pixel is high, thereby improving the reproducibility of the yellow pixel at the time when the yellow pixel is converted into a monochrome pixel.
However, In the color/monochrome conversion in which the reproducibility of the yellow pixel has been improved, there is such a problem that invisible yellow security information embedded in a copied matter is visualized by the monochrome copy. It is undesirable that the yellow security information is visualized by the copy.
In the Official Gazette of Japanese Patent Application Laid-Open No. 2003-283848, a countermeasure for solving such a problem that the yellow security information included in the original is reproduced by the monochrome copy is not disclosed.
To solve the foregoing problem, therefore, it is an object of the invention to provide image processing apparatus and method in which when an original including security information is read by a reading unit and is monochrome converted, such a monochrome output that the security information is not visualized can be performed.